const { Readable, Writable, Transform, pipeline } = require ( 'stream' );

const inStream = new Readable({
                                  read(size) {
                                      this.push(String.fromCharCode(this.currentCharCode++));
                                      if (this.currentCharCode > 90) {
                                          this.push(null);
                                      }
                                  }
                              });

inStream.currentCharCode = 65;

inStream.pipe(process.stdout);